Installing Packages to Salesforce Sandbox Orgs

Installing Package to Sandbox using the Package URL
From the package URL, replace the word “login” with “test” (see example below). Then complete the installation with your sandbox username/password

Replace:
https://login.salesforce.com/?startURL=%2Fpackaging%2FinstallPackage.apexp%3Fp0%3D0...

With:
https://test.salesforce.com/?startURL=%2Fpackaging%2FinstallPackage.apexp%3Fp0%3D...

Installing Package to Sandbox using the AppExchange Get It Now button
Click the Get It Now button from the AppExchange listing & make sure you select “Sandbox (text environments)” from the radio button. Then continue with the installation process.