fix: add edit users sending up wrong data

[kyle-ssg]

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Changes

When adding a group member, the FE was sending up all existing group members. This caused an issue where MANAGE_USER_GROUPS did not have appropriate permissions to add themselves to a group.

Also, if a change errors the FE was silently swallowing them instead of showing them.

How did you test this code?

Added and removed members during edit / creation of a group

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Project	Deployment	Actions	Updated (UTC)
flagsmith-frontend-preview	Ready	Preview, Comment	Mar 18, 2026 11:01am
flagsmith-frontend-staging	Ready	Preview, Comment	Mar 18, 2026 11:01am

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Ignored	Preview	Mar 18, 2026 11:01am

[github-actions]

Docker builds report

Image	Build Status	Security report
ghcr.io/flagsmith/flagsmith-e2e:pr-6923	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api-test:pr-6923	Finished ✅	Skipped
ghcr.io/flagsmith/flagsmith-api:pr-6923	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith:pr-6923	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-private-cloud:pr-6923	Finished ✅	Results ✅
ghcr.io/flagsmith/flagsmith-frontend:pr-6923	Finished ✅	Results ✅

[github-actions]

Playwright Test Results (oss - depot-ubuntu-latest-16)

 10 passed

Details

 10 tests across 7 suites
 30.6 seconds
 53c1820
 🔄 Run: #15235 (attempt 1)

[github-actions]

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 10 passed

Details

 10 tests across 7 suites
 54.1 seconds
 53c1820
 🔄 Run: #15235 (attempt 1)

[github-actions]

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 16 passed

Details

 16 tests across 13 suites
 57.3 seconds
 53c1820
 🔄 Run: #15235 (attempt 1)

[github-actions]

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 16 passed

Details

 16 tests across 13 suites
 28.5 seconds
 53c1820
 🔄 Run: #15235 (attempt 1)

[talissoncosta]

Hey @kyle-ssg , thanks for handling this! I've left two inline comments, they're not blockers, but since the goal of this PR is to stop swallowing errors silently, it felt worth flagging for consistency.

[kyle-ssg]

Hey @kyle-ssg , thanks for handling this! I've left two inline comments, they're not blockers, but since the goal of this PR is to stop swallowing errors silently, it felt worth flagging for consistency.

Done, I'd like to get this merged today if possible as it has been causing a real issue.

[github-actions]

Playwright Test Results (oss - depot-ubuntu-latest-16)

 10 passed

Details

 10 tests across 7 suites
 47.5 seconds
 d252b3a
 🔄 Run: #15334 (attempt 1)

Playwright Test Results (oss - depot-ubuntu-latest-arm-16)

 10 passed

Details

 10 tests across 7 suites
 28.8 seconds
 d252b3a
 🔄 Run: #15334 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-arm-16)

 1 passed

Details

 1 test across 1 suite
 58.3 seconds
 d252b3a
 🔄 Run: #15334 (attempt 1)

Playwright Test Results (private-cloud - depot-ubuntu-latest-16)

 1 passed

Details

 1 test across 1 suite
 1 minute, 3 seconds
 d252b3a
 🔄 Run: #15334 (attempt 1)

[talissoncosta]

Thanks for handling that @kyle-ssg ! Good job!