我不明白此错误：

Your requirements could not be resolved to an installable set of packages.

Problem 1
- don't install phpseclib/bcmath_compat 1.0.3|don't install php 7.3.13
- composer.json/composer.lock requires php 7.3.* -> satisfiable by php[7.3.13].
- Installation request for phpseclib/bcmath_compat 1.0.3 -> satisfiable by phpseclib/bcmath_compat[1.0.3].

我正在运行PHP 7.3.13。

有什么想法吗？