Microsoft startup and active Azure subscription.

Startup credits are applied at the billing-account/subscription level; they are not something that can be manually “connected” from the Azure side by a separate action.

To use Microsoft for Startups credits with an Azure subscription, the subscription must be created under the same billing account that holds the sponsorship/credits and must be associated with the account that activated the offer:

1. The individual who received the startup credit offer must activate it using their Microsoft Account (MSA). This activation creates an Entra tenant, an Azure subscription, and applies the credits to that subscription’s billing profile.
2. After activation, any subscriptions created under that billing account can use the sponsorship credits.
3. If there is already a pay-as-you-go subscription and the same MSA was used to activate the startup credits, credits will not automatically apply to that existing subscription unless both subscriptions share the same billing profile.
4. If the existing subscription is on a different billing profile or billing account, a support request is required to have Microsoft move or align the billing so the sponsorship credits apply to the desired subscription.

Given an active subscription and a separate startup credit offer, the practical next step is:

1. Sign in to the Azure portal with the MSA that received/activated the startup credits.
2. Go to Subscriptions and verify which subscription is associated with the sponsorship credits (created during activation).
3. If the credits are not being applied to the intended subscription, submit an Azure support request asking to link the existing subscription to the billing profile that holds the startup sponsorship credits or to move the sponsorship to the correct subscription.

If the startup credits have not yet been activated, they must be activated first using the instructions in the startup activation flow; once activated, subscriptions created under that billing account will automatically draw from the sponsorship credits.

References:

• Activate Azure Credits
• Properly Setting Up Your Azure Account
• Best Ways to Use Startup Credits
• I have an Azure Credit of 11000$$, but I have 2 billing accounts. The bill doesn't come to the right place. - Microsoft Q&A