4. Is there a ban on corporate donations to candidates?

Election Code of the Republic of Azerbaijan, 2003 (as amended 2019) https://www.msk.gov.az/uploads/qanunvericilik/Election-code_2020.pdf

Corporate donations are not banned, there are certain limits on them

ECode prohibits election funds of candidates and registered candidates receiving donations from the following sources:  State bodies and municipalities (Art. 90.2.7.); state and municipal organizations and offices (Art. 90.2.9.); legal entities (incluidng foreign interests), of which more than 30% of the charter (property) capital belongs to the state or municipality on the day of official publication of the decision to hold elections (Art. 90.2.6 and 90.2.9), military units (Art. 90. 2.10)., and charitable organizations , religious associations, institutions and organizations (Art. 90. 2.11). 

Donations received by parties, candidates or referendum campaign groups from the above-mentioned entities must be returned to the donor within 10 days of receipt, deducting the transfer expenses and indicating the reasons for return (Art. 93.5.)