Why is the error "Primary bank change cannot be processed online for your account. Please initiate request offline." displayed?

The error Primary bank change cannot be processed online for your account. Please initiate request offline is displayed for the following Zerodha accounts:

An individual account with a mobile number or email ID not linked to Aadhaar: Courier the account modification form (PDF) and the bank proof ¹ to Zerodha. Sample copy (PDF).
An Individual account linked with a proprietorship bank account: Courier the account modification form (PDF), banker's letter (PDF) and bank proof ¹ to Zerodha. Sample copy (PDF).
Joint Zerodha account: Courier the account modification form (PDF) and the bank proof ¹ to Zerodha. Sample copy (PDF).
Clients who do not have a Zerodha demat account: Courier the account modification form (PDF) and the bank proof ¹ to Zerodha.
NRE and NRO -PIS account: Courier the account modification form (PDF), self-attested new PIS letter and the self-attested PIS bank proof ¹ to Zerodha. Sample copy (PDF).
Non-individual accounts (HUF, corporate, partnership, Limited liability partnership, AOP, trust): Courier the account modification form (PDF) and the bank proof ¹ signed by the authorised signatory with seal and stamp to Zerodha. Sample HUF (PDF), corporate (PDF), partnership (PDF), LLP (PDF) forms.

Ensure that the signature on the documents matches the signature in the account. To know the existing signature proof in the account, see Where can the submitted documents be checked while opening an account?

Courier the documents to:

Zerodha Customer Support Centre,
680, Fortuna 1, 15th Cross Road,
8th Main Road, 2nd Phase, J. P. Nagar,
Bengaluru, Karnataka, 560078

The new primary bank will be linked within 72 hours, and Zerodha will send a confirmation email. ₹25 + GST is charged to change the primary bank account. A maximum of three bank accounts can be linked to the trading account, one primary and two secondary.

Notes :

¹ Bankproof can be any one of the following:

Personalised cancelled cheque with the name printed on the cheque leaf.
Self-attested bank statement with the IFSC and MICR clearly visible.
Self-attested bank passbook.

Did you know? PayTM payments bank cannot be linked to a Zerodha account. To learn why, see Can PayTM payment bank be linked to Zerodha?