Hi,
Unfortunately credits cannot be used to pay for third-party offerings. Below is excerpt from Azure Sponsorship Offer details:
Exclusions
Special pricing does not apply to Microsoft Azure support plans, third-party branded products, products sold through Microsoft Azure Marketplace, or products otherwise sold separately from Microsoft Azure (for example, Active Directory Premium). Tiered pricing does not apply to sponsorship; all services are billed at flat PAYG rates which are utilized through sponsorship credits. You will be responsible for all charges incurred for these services and products.
And below is excerpt from Microsoft for Startups Azure Credit Offer:
Azure credits can be applied toward any Azure product listed here. Azure credits can't be used for non-Azure products, products purchased through Microsoft Azure Marketplace, or Microsoft Support Plans.
The details of your Azure sponsorship offer type can be found at azure.microsoft.com/pricing/offers/ms-azr-0036p/.
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP