The income tax department has sent out emails about past financial years, mentioning that some deductions claimed under Section 80G are not allowed because the Donee PAN entered isn’t eligible. Often, this is just a mix-up. Donations that should be claimed under Section 80GGC or 80GGB (which allows for 100% deductions) have mistakenly been claimed under Section 80G (which also offers 100% deductions).
Here’s my take: This is a mistake that can easily be fixed under Section 154. You should file for rectification and move the amount to the correct section (80GGC or 80GGB instead of 80G). You can apply for rectification within four years after the end of the relevant Assessment Year, and it will be processed by the Central Processing Centre (CPC). If your rectification isn’t accepted online, you can take it to your jurisdictional Assessing Officer (AO).
Using an Updated Return (under Section 139(8A)) should be the last option because it requires declaring extra income and paying additional tax, even though the deduction is valid. source form