Preferred Chain

Using --preferred-chain to select the alternate chain.

If the ACME CA provides multiple cert chains, you can use --preferred-chain to select one. Otherwise, it will get the default chain.

1. For letsencrypt.org Staging Server:

https://letsencrypt.org/docs/staging-environment/

There are 2 chains provided:

Name	Default
(STAGING) Pretend Pear X1	No
(STAGING) Bogus Broccoli X2	Yes

You select the chain like:

acme.sh  --issue -d example.com .....  --test    --preferred-chain  "(STAGING) Pretend Pear X1"

You can also use part of the name:

acme.sh  --issue -d example.com .....  --test    --preferred-chain  "X1"

It's also case-insensitive:

acme.sh  --issue -d example.com .....  --test    --preferred-chain  "x1"

2. For Letsencrypt.org Production server:

   There are 2 chains provided:

   Name	Default
   DST Root CA X3	Yes
   ISRG Root X1	No

   You select the chain like:

acme.sh  --issue -d example.com .....  --server letsencrypt   --preferred-chain  "ISRG Root X1"

You can also use part of the name:

acme.sh  --issue -d example.com .....  --server letsencrypt   --preferred-chain  "ISRG"

It's also case-insensitive:

acme.sh  --issue -d example.com .....  --server letsencrypt    --preferred-chain  "isrg"

3. You can also set the default preferred chain for a specified CA(from v3.0.1).

acme.sh --set-default-chain  --preferred-chain "ISRG"   --server  letsencrypt

When you request a cert from letsencrypt in future, it will use the default preferred chain.