Please note that we have not much influence on whether Gmail classifies an email as promotion or spam. It largely depends on the text your email contains.
Common trigger words for Gmail to categorize an email as «Promotions» are:
- Pay now
- Free gift card
- Gamble etc.
Here is more information on how to avoid an email landing in the «Promotions» tab: https://bizbudding.com/why-emails-going-into-gmail-promotions-tab/