Make sure you are not in spawn protection. If you wish to build within spawn protection, make sure you are op first.
What is sais when i type /version Code: [12:58:18] [Server thread/INFO]: This server is running PocketMine-MP 1.7dev-70 「[REDACTED]」 implementing API version 3.0.0-ALPHA8 for Minecraft: PE v1.2.0.81 (protocol version 137)
That's a non-release build. At the minimum you should be using build 83 (ALPHA8 release) and preferably build 318 (ALPHA9 release).
ALPHA-9 REL: https://jenkins.pmmp.io/job/PocketMine-MP/318/artifact/PocketMine-MP_1.7dev-318_716c1f29_API-3.0.0-ALPHA9.phar Dev Version: https://jenkins.pmmp.io/job/PocketM...-MP_1.7dev-403_5178373d_API-3.0.0-ALPHA9.phar
Okay, did you replace your phar with the phar posted above? You might also need to replace your bin folder with https://ci.appveyor.com/api/buildjobs/45h78e5l5wx1wu37/artifacts/php-7.2.0RC5-vc15-x64.zip.