WLAN Sniffing, Can't Find GET and POST Data

Hello,

I tried to follow this article: null-byte.wonderhowto.com/how-to/stealthfully-sniff-wi-fi-activity-without-connecting-target-router-0183444/

I did everything as described in this article. I first put my Wireless card in Monitor Mode, then sniffed the traffic of the target WLAN, did setup wireshark and load the .cap file. Its loading some traffic into wireshark, but as soon as I use any filter to get the GET or POST requests, it doesn't show anything. I have make sure to visit some GET websites and send out some registrations forms for a newsletter or similar to also get some POST entries while capturing the traffic of my WLAN. But somehow I don't get anything. Maybe someone can help me out here?