Maze allows you to conduct user testing with the prototypes you've already imported. If you've imported your prototype but are missing screens, these steps may help you resolve the problem.
Most issues with mising screens occur when creating the share link in the prototype tool. If you're missing screens after importing a prototype to Maze, the first thing to check is whether the share link you generated in your prototyping tool is restricted to a subset of screens.
Review the documentation for your prototyping tool and verify that you have generated an unrestricted share link. For example, in Marvel you can generate a share link to a specific section while in InVision you can share only a specific set of screens.
For InVision especially, be sure that you have generated your share link as described in How do I share my InVision prototype, board, or freehand?, and not using other methods InVision offers which limit the share to a specific subset of screens.