It is common to have an issues when you write a plugin, especially if you do this for the first time. This is why debugging them is very important. The first step for debugging is to set an environment variable when running radare2 instance:
R_DEBUG=yes r2 /bin/ls
Loading /usr/local/lib/radare2/2.2.0-git//bin_xtr_dyldcache.so
Cannot find symbol 'radare_plugin' in library '/usr/local/lib/radare2/2.2.0-git//bin_xtr_dyldcache.so'
Cannot open /usr/local/lib/radare2/2.2.0-git//2.2.0-git
Loading /home/user/.config/radare2/plugins/asm_mips_ks.so
PLUGIN OK 0x55b205ea6070 fcn 0x7f298de08762
Loading /home/user/.config/radare2/plugins/asm_sparc_ks.so
PLUGIN OK 0x55b205ea6070 fcn 0x7f298de08762
Cannot open /home/user/.config/radare2/plugins/pimp
Cannot open /home/user/.config/radare2/plugins/yara
Loading /home/user/.config/radare2/plugins/asm_arm_ks.so
PLUGIN OK 0x55b205ea6070 fcn 0x7f298de08762
Loading /home/user/.config/radare2/plugins/core_yara.so
Module version mismatch /home/user/.config/radare2/plugins/core_yara.so (2.1.0) vs (2.2.0-git)
Loading /home/user/.config/radare2/plugins/asm_ppc_ks.so
PLUGIN OK 0x55b205ea6070 fcn 0x7f298de08762
Loading /home/user/.config/radare2/plugins/lang_python3.so
PLUGIN OK 0x55b205ea5ed0 fcn 0x7f298de08692
Loading /usr/local/lib/radare2/2.2.0-git/bin_xtr_dyldcache.so
Cannot find symbol 'radare_plugin' in library '/usr/local/lib/radare2/2.2.0-git/bin_xtr_dyldcache.so'
Cannot open /usr/local/lib/radare2/2.2.0-git/2.2.0-git
Cannot open directory '/usr/local/lib/radare2-extras/2.2.0-git'
Cannot open directory '/usr/local/lib/radare2-bindings/2.2.0-git'
USER CONFIG loaded from /home/user/.config/radare2/radare2rc
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