I try add Child NS for .com domain, but got error "This action can't be performed on this domain."

Because .com domains can be registered via several registrars, there are some differences:

Child Name Servers registration is available for the registrars:

• PDR Ltd. d/b/a PublicDomainRegistry.com
• Alibaba Cloud Computing (Beijing) Co., Ltd. (hichina.com / net.cn / aliyun.com)

Note: You can read the instructions for Registering and Managing Child Name Servers in our knowledge base.

Child NS registration is not available for registrars:

• Internet X aka PSI-USA, Inc. dba Domain Robot (internetx.com / psi-usa.info)
• GMO Internet Group Ltd. d/b/a Onamae.com (gmo.jp)
• NICENIC INTERNATIONAL GROUP CO., LIMITED (www.nicenic.net)

When trying to register child name servers, these registrars respond with the error "This action can't be performed on this domain."

Unfortunately, this additional option is not implemented on the side of these registrars, but you can contact the registrar support to manually register child name servers or you can use any name servers except child ones.

Note: When renewing .com domains for the first time, the registrar will automatically change to PDR Ltd. and the  to create Child NS option will become available from the control panel.