Get earliest start date for membership

GET /api/memberships/earlieststartdate

Success: 200 OK

Products: Operator (FOH), Consumer (CONSUMER) (any one of these products, not all)
Features: Online Joining (ONLINEJOIN), Front of House Generic Access (FOHGENERIC) (any one of these features, not all)

Overview

Works out the earliest date a membership may start, given the membership types being bought and the site they are being bought at. Call it before you build a date picker or send a startDate to Create a membership for a member — membership types can carry their own not-before date, and a site that has not opened yet imposes one of its own.

The rule that catches people out is that the constraint is relaxed, not tightened, by a missing date. If every membership type you name carries an earliest start date, the answer is the latest of them. If even one of them carries none, the membership type dates are discarded entirely and the answer falls back to the site's opening date. Either way the result is never in the past: it is floored at today.

All dates are compared and returned with the time component stripped, and "today" is the server's current date rather than yours — near midnight, or from another time zone, expect the boundary to move.

Endpoint

GET {base_url}/api/memberships/earlieststartdate

{base_url} is the environment URL issued to your integration. See Authenticating with Gladstone APIs.

Query parameters

Name	Type	Required	Description
`membershipTypeIds`	string	Yes	The membership types being bought, as a comma-separated list — for example `ADULT,CHILD`. Take the ids from `[].id` in Get membership types grouped by tag. Matched case-insensitively. Although not marked as required, omitting it fails with `400` and `Please provide at least 1 or more membershipTypeIds`. The same id twice fails with `Request contains duplicate membershipTypeIds in route`, and any id that does not resolve fails the whole call with `404` and `One or more of the membershipTypeIds provided are invalid` — you are not told which one.
`siteId`	string	Yes	The site the membership will be sold at. Its opening date is the fallback constraint used whenever any of the named membership types has no earliest start date of its own. Despite being marked optional, omitting it fails with `400` and `Please provide a siteId`, and a site that does not exist fails with `404` and `siteId '{siteId}' does not exist`.

Sample request

cURL

curl -X GET '{base_url}/api/memberships/earlieststartdate' \
  -H 'Authorization: Bearer {accessToken}' \
  -H 'X-Use-SSO: true'

Response fields

Field	Type	Description
`siteOpeningDate`	string (date-time)	The date the site opens or opened, with the time component zeroed. `null` when the site has no opening date recorded, which the platform treats as no constraint. Returned for context: it only feeds into `earliestStartDate` when at least one membership type has no earliest start date of its own.
`membershipTypes`	array of object	The membership types you asked about and the constraint each one carries, in the order the platform resolved them. Use it to explain the answer to a user — it is the only way to see which type is responsible for a late `earliestStartDate`, or that one has no constraint and so relaxed the calculation to the site opening date.
`membershipTypes[].id`	string	The membership type id, echoing one of the values you sent in `membershipTypeIds`.
`membershipTypes[].earliestStartDate`	string (date-time)	The not-before date configured against this membership type, with the time component zeroed. `null` means the type imposes no constraint — and a single `null` anywhere in this array changes the whole calculation, causing every other type's date here to be ignored in favour of `siteOpeningDate`.
`earliestStartDate`	string (date-time)	The answer: the earliest date a membership of these types may start at this site, with the time component zeroed. Never `null` and never in the past. When every entry in `membershipTypes` has an `earliestStartDate`, this is the latest of them, floored at today. When any entry has `null`, it is `siteOpeningDate` floored at today — which reduces to today whenever the site has already opened or has no opening date.

Sample response

200 OK

{
  "siteOpeningDate": "2026-08-14T19:00:00Z",
  "membershipTypes": [
    {
      "id": "string",
      "earliestStartDate": "2026-08-14T19:00:00Z"
    }
  ],
  "earliestStartDate": "2026-08-14T19:00:00Z"
}

Errors

Status	Meaning	When
`400`	Bad request	`Please provide at least 1 or more membershipTypeIds` — the parameter is missing or empty.
`400`	Bad request	`Please provide a siteId` — the parameter is missing or empty.
`400`	Bad request	`Request contains duplicate membershipTypeIds in route` — the same id appears more than once, compared case-insensitively.
`404`	Not found	`One or more of the membershipTypeIds provided are invalid` — at least one id matched no membership type. The message does not say which.
`404`	Not found	`siteId '{siteId}' does not exist`
`500`	Internal server error	An unexpected server-side failure. Unusually for this platform, the response body contains the error message.

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