I develop 3 unpublish Google Apps Marketplace(v1) applications that use Google Provisioning API with same scopes(prov_user, prov_group, prov_nickname and contact). There was no problem where I run 3 applications three months ago, There are problem that 403 "Invalid OAuth Target" has occurred in the 2 applications.
I confirmed Marketplace v1 and Installed Google Apps settings but these has not changed from three months ago.
I think that the best solution is migration to Marketplace v2 and Directory API but I can not right now there for various reasons. I want you to tell me the solution use Marketplace v1 and Provisioning API.
It would be a poor idea to use the provisioning api at this point, since the provisioning api has been marked as deprecated, https://developers.google.com/google-apps/provisioning/.
Apps that are currently published and installed will into a domain will work for a while, but new customers/domains will not. You're best bet is to switch to the Directory api as soon as you can.