Why Hashem did not accept the Cain sacrifice? what were Cain's mistakes before bringing sacrifice? If Cain did Tshuva will Hashem accept his sacrifice? did Cain ever prayed?

ב"ה Shalom It's close to Shabbat and I just wanted to answer you quickly. Based on the commentaries of Rashi and Radak, and the Netziv, Cain did indeed pray but since his intentions were not sincere and his offering was from the worst and cheapest part of his crop, Hashem did not accept his prayer or offering. All the Best and Shabbat Shalom