Hello Jeni,
my name is Manuel and I am an independent advisor.
The form is probably set to "only people in my organization can respond".
Therefore make sure your colleagues are definitely logged in on the correct tenant (******@TENANT.onmicrosoft.com).
This was a common issue in my environment.
If it is still not working you could share it with anyone who has the link (if it is no confidential form) and pass it to the concerned users.
This article describes how to adjust the settings for sharing a form:
https://support.office.com/en-us/article/adjust...
I hope this helps.
Greetings,
Manuel