May I upload a proof of use at a later stage?

The fact that you can upload proof of use at a later stage: this will be implemented in the coming weeks and shall no longer be done through customer support.

FAQ

API (Automated Interface)

billing

correction process

documentary evidence

general

invoicing

Mark Record Transfer

mark record verification

New gTLD program

Notifications

official agents

online payment

OT&E

prepayment account

pricing

proof of use

Registrars

Registries

Renewal

Signed Mark Data (SMD)

Strawman Model - Abused Labels

Sunrise Services

support

trademark claims services

Trademark Clearinghouse Certificate Authority

Trademark Eligibility Requirements

trademark submission

TREx Service

user registration