In a German textbook I see a sentence:
Er freut sich über dein Besuch.
Dein is a possesive article following variation like indefinite article. Dein is nominitive form. Why is it not in accusative (deinen) or dative (deinem) form?
That first sentence from the textbook is definitely wrong. I saw many German textbooks abroad, which seem to never have been proofread by a native speaker, let alone a linguist. Sometimes such false sentences are part of exercises, but then this should be clearly marked.
The pronoun has to be in accusative case:
Er freut sich über deinen Besuch.
(ask: Er freut sich über wen/was?)