BD3QYZ The Dely solid adhesive stick works well for both sealing envelopes and attaching postage stamps.
BH3HMN_Chen Common adhesive tape, but it feels not very secure. Liquid glue is better. It's best to find a scraper and apply a few drops of glue evenly.
debain You can simply apply it directly with a solid adhesive stick, or you can also use liquid glue.