question

First, the merchant id you are using does not exist in sandbox, it exists in prod. You need to make sure you are making calls to the correct environment.

To obtain a token, login to your test merchant's dashboard. You should see your application which appears to be named "test" in the left side nav (if installed to your merchant correctly). Hit the test link and you will be redirected to your application (even if your app url is not set correctly). The access_token will be in the URL. This works because your application is set to use "Token" for its Default OAUTH response, which is for testing only.

Using a valid, non-testing token is not much harder. First login to your developer dashboard. Select your application "test" (from the left nav) and then select the edit icon next to REST Configuration. Set the value for Default OAUTH Response to code instead of token and save the changes. Next follow the steps in the second paragraph above. This time instead of seeing an access_token in the url you will see a code. Now you will need to obtain an access_token from the code. Make a REST call to the Clover API outlined in Step 3 - Request an API Token - https://docs.clover.com/clover-platform/docs/using-oauth-20. You will need your app id, app secret and the code from above. The response of this call will be your access_token.

Note: If you are trying to make API requests from a web browser you will need to set the CORS Domain correctly or else the browser will reject the request.