The steps differ depending on your payment method.
For in-app purchases
For website payments
For in-app purchases
You can sign up for Pastela Plus through the app’s plans page.
Open the Pastela app and go to Settings > Plan settings > Change plan to access the plans page.
For website payments
You can sign up for Pastela Plus through the website (Pastela Cloud)’s plans page.
*When opening the page, make sure to log in with the Pastela (pixiv) account you wish to use for Pastela Plus.