Cannot add multiple PGP keys (Base64 error)

What is the correct process for adding another PGP key? (on website with command line commands)

I tried to just select "update my key" paste my current key and the public key of another key.
I could continue and got this command:

curl \
  --data-urlencode sig="`\
   echo '{"body":{"key":{"eldest_kid":"0101f8e0993c69511b515baf988e36c1a20db7cd576710e3c1dcab335a6ecded58370a","fingerprint":"7046c1b286449eaf9f3ff5c18f162ae44088f1be","host":"keybase.io","key_id":"8f162ae44088f1be","kid":"0101f8e0993c69511b515baf988e36c1a20db7cd576710e3c1dcab335a6ecded58370a","uid":"b9ac048da91260baa2c4db3a53747f19","username":"rugk"},"pgp_update":{"fingerprint":"7046c1b286449eaf9f3ff5c18f162ae44088f1be","full_hash":"6ca6609adef46260d41b6b702fed947077b4d26ce318fe40f41e5edda3f45682","kid":"0101f8e0993c69511b515baf988e36c1a20db7cd576710e3c1dcab335a6ecded58370a"},"type":"pgp_update","version":1},"ctime":1507023806,"expire_in":157680000,"prev":"d8b69e80e84cd17efd281b13c6f253a10447ba0d99f81dbb475122dd247c63cb","seqno":5,"tag":"signature"}' | \
   gpg2 -u '7046c1b286449eaf9f3ff5c18f162ae44088f1be' -a --sign`" \
  --data-urlencode type="pgp_update" \
  --data-urlencode session="lgHZIGI5YWMwNDhkYTkxMjYwYmFhMmM0ZGIzYTUzNzQ3ZjE5zlnTVufOAeEzgNkgZTFlODMzYzVlNjliM2U5YmZlOGM1YmFkYTI5MmI0MDLEILVRHi/lfRNZx1HukL48A+AMpxsgNtxMIYLuDPm7ov8t" \
  --data-urlencode csrf_token="lgHZIGI5YWMwNDhkYTkxMjYwYmFhMmM0ZGIzYTUzNzQ3ZjE5zlnTVrTOAAFRgMDEIOWY5s8t64wZ/1OblfOv0dWlKEJDdo++RJJBCF6nMY4x" \
  --data-urlencode plain_out="1" \
  --data-urlencode signing_kid="0101f8e0993c69511b515baf988e36c1a20db7cd576710e3c1dcab335a6ecded58370a" \
  --data-urlencode public_key="-----BEGIN PGP PUBLIC KEY BLOCK-----

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i2+ByVW0qwsgNywZoUDLfYwwnJb78tg+gtD73rOQPzWgIgUKAX6GZGtAIrQ7cKk3
R+ysrYDTBVZujdRtCUoJao363ETDn8ott2Eptd0Am+ggXUuOs3gIt5Po5tJh6zTU
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3FZ14rcMyI/kiCdODSAGDBhsAIJg6Uu9iQEMghFXlMsG7ngSq8LP9vL48en69VRI
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SxqqxQNX3VGBnRi19mI5xA2KygItdXcA0W95D1J4qla+85ZqbHHqaqWGcQARAQAB
tBVydWdrIDxydWdrQHBvc3Rlby5kZT6JAjUEEAEIACkFAlkM2okGCwkIBwMCCRCP
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qavli0RaU+jKjjbuB6u/j9nnPv0Trchsojy8v+9T1hwvNjdoeJJWhXrWHpvOwAX6
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/0X8su31w8i8Y4DA6chw+Qwr+2SA+nHHUS565YsNcjPsG3hJWCEDy6FMXwcI5Jmf
7bj0gKKe6lcFaoigo98T1Y0bt/OWHBA0jzQfWJFGFq3Cy+YR25zKZXrQA60feiks
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FhQ/60OsnPECjz3Pb1y7fsQUOECVpprjE6JVbHHBan0t
=5UHP
-----END PGP PUBLIC KEY BLOCK-----
-----BEGIN PGP PUBLIC KEY BLOCK-----

mQINBFfIWIwBEADiNf/o13G2RlKSSQH5sriR5ReRwZ6rbuZjisaJzmQ9KKu7o+a9
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6A==
=C/5x
-----END PGP PUBLIC KEY BLOCK-----
" \
  --data-urlencode is_update="true" \
  --data-urlencode sig_required="true" \
  https://keybase.io/_/api/1.0/key/add.json

However, it ends with a Base64 error.

Error in your post
-------------------

Code: 100
Name: INPUT_ERROR
Description: bad base 64 string

Fedora 26
curl 7.53.1

Start by reproducing the website-generated curl request against https://keybase.io/_/api/1.0/key/add.json with the two PGP public keys and the shown gpg2 signing command. Investigate the key-add API entry point and the handling of the public_key or signature fields; done means adding multiple PGP keys no longer returns the bad base 64 string error.