自定义函数调用未启用，求大佬支援

<p>想通过上一接口返回的值中的某个内容作为下一个接口的入参，如下图：</p><p>上一接口返回内容：</p><p>"data:image/png;base64,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"</p><p>想要取，后的第二个值作为下一个接口的入参，写了如下参数</p><p><img src="http://talk-cdn.liumatest.cn/47ce779e-6e54-439b-8aa0-52b3b9de4194.png" style="max-width:100%;"><br></p><p><br></p><p>启用方法如下：</p><p><img src="http://talk-cdn.liumatest.cn/55f0eb24-01f2-4c2a-81cb-5fc5bb291719.png" style="max-width:100%;"><br></p><p>执行未能成功取到对应值</p><p><img src="http://talk-cdn.liumatest.cn/79bca04f-ca87-403d-aa65-3b71d2ad7578.png" style="max-width:100%;"><br></p><p>用例中已经导入了该函数，求大佬帮忙看看哪里有问题。</p>