LTI Launch error when trying to launch

[YuvalYellin]

We are developing an LTI tool that already works well in Canvas in production in an institution and in out own env (https://exlibris.instructure.com/ ) 

We are now trying to integrate with a Test instance of another institution, and we are getting this Launch Error screen. 

My setup of the LTI side is as followed: 

"accesstokenEndpoint": "https:///sso.test.canvaslms.com/login/oauth2/token",

"authConfig": {

"method": "JWK_SET",

"key": "https:///sso.test.canvaslms.com/api/lti/security/jwks"

},

"authEndpoint":"https:///sso.test.canvaslms.com/api/lti/authorize_redirect",

"clientId": ...

"url": "https://canvas.test.instructure.com"

Hpwever, unlike our own production instance, the authorize_redirect doesn't seem to work as expected - in the production instance , when doing an authorizd_redirect request we are then redirected to the production instance url  ( https://[our instauction url/api/lti/authorize?..  ) and everything works. 

In the test Canvas instance we are now using, we are instead redirected to 

https://calstatela.test.instructure.com/api/lti/authorize?..., and then getting the launch error. 

Is there something wrong with the setup? should we use another url ? How can we know what's the real issue here?