A portal URL is an address used by certain device or player systems to reach a service interface. Some arrangements also use device registration information. It is not interchangeable with every M3U address or username-and-password login, and a portal workflow needs support from both the chosen player and the service.
A practical example
A set-top box can be configured with a portal address, while a phone app for the same household may require a different supported login format. The existence of one method does not make every other method automatically available for that account.
A common misunderstanding
Do not copy another customer's portal or alter device identifiers to force access. Request the correct supported setup method for the account and device being configured.
Related terms
Stable technical definition. Editorial approach