[BUG] Creating reimbursement requests with an invalid vendor should display an error on the client

[jasonappah]

Describe the bug

When submitting a reimbursement form with an invalid input for vendor, the page will display a 'request submitted successfully' alert, but the reimbursement is not actually saved, and an error is shown in the server logs.

To Reproduce
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1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
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Additional context
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