We encountered the same issue as was answered in this question: http://community.auth0.com/questions/3944/error-grant-type-password-not-allowed-for-the-clie Using the management API we can set the grants to what we want for the client and it works again. The problem we are having is that if anyone…

We've had to add some legacy client grants to an old client manually, they keep getting erased.

Topic		Replies	Views
Editing UI callback urls resets grants Get Help callback-urls , grants , ui , dashboard , bugs	3	4181	March 2, 2018
Can't add password grant type from Management API Get Help bug	3	3226	April 30, 2020
Unable to enable the refresh_token legacy grant type Get Help auth0-configuration , refresh-tokens , grant-types	4	4651	March 2, 2018
V7 Auth0.js Passwordless Auth Failed Get Help passowordless	2	3681	March 2, 2018
GrantType Resource Owner Password not allowed Get Help grant-types	4	5570	March 2, 2018