You can't share a VPC subnet

Scenario

When you attempt to use AWS RAM to share a VPC subnet with another account, the sharing operation succeeds. However, the consuming account shows LIMIT EXCEEDED for that resource in the AWS RAM console.

Cause

Some individual resource types have service-specific restrictions separate from the restrictions enforced by AWS RAM. Some of those restrictions can effectively prevent sharing even if you haven't reached one of the restrictions in AWS RAM. Limits are an example of these restrictions. Amazon Virtual Private Cloud (Amazon VPC) limits the number of subnets that you can share with another individual account. If you try to share a subnet with a consuming account that already contains the maximum number of subnets, then that consuming accounts displays LIMIT EXCEEDED in the console for that resource. For more information about this limit, see Amazon VPC Quotas – VPC sharing in the Amazon Virtual Private Cloud User Guide.

To address this, first check for other resource shares that might be sharing the specified resource with the affected account, and remove those shares that you might no longer require. You can also request an increase for a limit that supports adjusting. Use the Service Quotas console to request a limit increase.