The link needs to be a valid slug, and “/about-us.html/” is not a valid slug. The period . is disallowed in slug names.
A slug should consist only of lowercase alphanumeric characters [a-z, 0-9], dashes -, and underscores _. In addition the following rules apply: you cannot have two or more dashes in a row, however sequences of underscores are permitted, and a slug cannot start or end with a dash.
Detailing the info suggested here when having issues will help the community to provide the best possible help as quickly and as efficiently as possible.
Have you checked the following post ?
It goes about the same issue and some solutions are provided (specially this one by @luisherranz )
Actually I have already finished my site without .html url. so i have question for i think i will add .html url then any effect for my current code or API.